1. Field of the Invention
The present invention relates to a laser printer, and more particularly, to a laser printer using a photosensitive belt having a seam.
2. Description of the Related Art
In general, in a laser printer, developer is coated on a photosensitive belt to form an image, and then the image developed on the photosensitive belt is transferred to a roller to print the image on a sheet of paper.
An example of a laser printer is schematically illustrated in FIG. 1. The laser printer includes a transfer backing roller 11a, a steering roller 11b and a driving roller 11c. An photosensitive belt 12 is rotatably installed around the rollers 11a, 11b and 11c.
At one side of the photosensitive belt 12, there is an eraser 23 for erasing image information of a previous step, and a charger 24 for uniformly electrifying the photosensitive belt 12 passing through the eraser 23. The image information recorded on the photosensitive belt 12 of the previous step is erased by the eraser 23, and then the charger 24 applies a predetermined voltage to the photosensitive belt 12 to be charged.
Also, at one side of the photosensitive belt 12, of a color printer, passing between the steering roller 11b and the driving roller 11c, there is a plurality of laser scanners 25 and developing devices 26 for combining colors. The laser scanner 25 scans light corresponding to received image information to form a photosensitive region on the photosensitive belt 12. In the developing device 26, a developer is coated on the photosensitive region formed by the laser scanner 25.
The image developed on the photosensitive belt 12 is transferred to a transfer roller 17 to print an image on a sheet of paper 19 by being pressed by a pressure roller 18.
Here, the photosensitive belt 12 is a loop type belt, and has a seam 12a where end portions of the belt 12 overlap. As the photosensitive belt 12 circulates along the rollers 11a, 11b and 11c, the seam 12a of the photosensitive belt 12 can be caught between the transfer backing roller 11a and the transfer roller 17. Also, some of the developer may remain at the seam 12a, to thereby contaminate the paper 19.
Accordingly, in the conventional art, when the photosensitive belt 12 passes between the transfer backing roller 11a and the transfer roller 17, the transfer roller 17 and the pressure roller 18 separate a predetermined distance from the backing roller 11a, to thereby prevent the seam 12a from being caught.
During printing, since the transfer roller 17 is coupled with the pressure roller 18, the two rollers 17 and 18 should operate simultaneously. Thus, much time is required for operation, and the structure of the mechanism for controlling the distance between the transfer roller 17 and the backing roller 11a is complicated.